As soon as Kubuntu 10.4 came out at the end of April I did a clean reinstall. However, Kdenlive now runs quite a lot slower than before (9.10). From the limited testing I've done, rendering is up to four times slower and during editing the interface is a lot less responsive. For example, the pause button takes up to a second to respond.

Other problems:

1 During preview, as the window scrolls the cursor leaves occasional debris behind (copies of itself).

2 The audio waveforms don't appear unless I go to "Configure Kdenlive" then immediately return.

Anyone else had a similar experience?

My system is an ASUS F5L series laptop with a Core 2 Duo processor and 2GB of main memory.

Regarding the waveforms, toggling the "Show audio thumbnails" (i.e. two clicks) also brings them up. But I have to do it each time I start Kdenlive.

For me kdenlive isn't slower than before.
However I also have the two other problems you described.
I will have a look at them.